This section is intended to introduce the reader to various aspects of art, which may be associated with embodiments of the present invention. This discussion is believed to be helpful in providing the reader with information to facilitate a better understanding of particular techniques of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not necessarily as admissions of prior art.
The oil and gas industry incurs substantial operating costs to drill wells in the exploration and development of hydrocarbon resources. The cost of drilling wells may be considered to be a function of time due to the equipment and manpower expenses being based on time. The drilling time can be minimized in at least two ways: 1) maximizing the Rate-of-Penetration (ROP) (i.e., the rate at which a drill bit penetrates the earth); and 2) minimizing the non-drilling rig time (e.g., time spent tripping equipment to replace or repair equipment, constructing the well during drilling, such as to install casing, and/or performing other treatments on the well). Past efforts have attempted to address each of these approaches. For example, drilling equipment is constantly evolving to improve both the longevity of the equipment and the effectiveness of the equipment at promoting a higher ROP. Moreover, various efforts have been made to model and/or control drilling operations to avoid equipment-damaging and/or ROP limiting conditions, such as vibrations, bit-balling, etc.
Many attempts to reduce the costs of drilling operations have focused on increasing the ROP. For example, U.S. Pat. Nos. 6,026,912; 6,293,356; and 6,382,331 each provide models and equations for use in increasing the ROP. In the methods disclosed in these patents, the operator collects data regarding a drilling operation and identifies a single control variable that can be varied to increase the rate of penetration. In most examples, the control variable is Weight On Bit (WOB); the relationship between WOB and ROP is modeled; and the WOB is varied to increase the ROP. While these methods may result in an increased ROP at a given point in time, this specific parametric change may not be in the best interest of the overall drilling performance in all circumstances. For example, bit failure and/or other mechanical problems may result from the increased WOB and/or ROP. While an increased ROP can drill further faster during the active drilling, delays introduced by damaged equipment and equipment trips required to replace and/or repair the equipment can lead to a significantly slower overall drilling performance. Furthermore, other parametric changes, such as a change in the rate of rotation of the drillstring (RPM), may be more advantageous and lead to better drilling performance than simply optimizing along a single variable.
Because drilling performance is measured by more than just the instantaneous rate of penetration, methods such as those discussed in the above-mentioned patents are inherently limited. Other research has shown that drilling rates can be improved by considering the Mechanical Specific Energy of the drilling operation and designing a drilling operation that will minimize the Mechanical Specific Energy (MSE). For example, U.S. Patent Publication No. US2008-0105424 and International Publication No. WO2007/073430, each of which is incorporated herein by reference in their entirety for all purposes, disclose methods of calculating and/or monitoring MSE for use in efforts to increase rate of penetration. Specifically, the MSE of the drilling operation over time is used to identify the drilling condition limiting the rate of penetration, often referred to as the founder limiter. Once the founder limiter has been identified, one or more drilling variables can be changed to overcome the founder limiter and increase the ROP. As one example, the MSE pattern may indicate that bit-balling is limiting the ROP. Various measures may be taken to clear the cuttings from the bit and improve the ROP, either during the ongoing drilling operation or by tripping and changing equipment.
Recently, additional interest has been generated in utilizing artificial neural networks to optimize the drilling operations, for example U.S. Pat. No. 6,732,052 B2, U.S. Pat. No. 7,142,986 B2, and U.S. Pat. No. 7,172,037 B2. However the limitations of neural network based approaches constrain their further applications. For instance, the result accuracy is sensitive to the quality of the training dataset and network structures, the optimization is based on local searches and that it may be difficult to process new or highly variable patterns.
In another example, U.S. Pat. No. 5,842,149 disclosed a close-loop drilling system intended to automatically adjust drilling parameters. However, this system requires a look-up table to provide the relations between ROP and drilling parameters. Therefore, the optimization results depended on the effectiveness of this table and the methods used to generate this data, and consequently, the system may lack adaptability to new drilling conditions which were not included in the table. Another limitation is that downhole data is required to perform the optimization.
While these past approaches have provided some improvements to drilling operations, further advances and more adaptable approaches are still needed as hydrocarbon resources are pursued in reservoirs that are harder to reach and as drilling costs continue to increase. Further desired improvements may include expanding the optimization efforts from increasing the ROP to optimizing the drilling performance measured by a combination of factors, such as ROP, efficiency, downtime, etc. Additional improvements may include expanding the optimization efforts from iterative control of a single control variable to control of multiple control variables. Moreover, improvements may include developing systems and methods capable of recommending operational changes during ongoing drilling operations.
While such research objectives can be readily appreciated when considered in this light, there are several challenges in achieving any one of these goals. For example, improved systems and methods should be able to correctly model dynamics between changes in drilling variables and the consequences in ROP and/or MSE (or other measurable parameter of drilling performance). Improved systems and methods may additionally or alternatively be adapted to identify efficient and safe zones of operations in light of the multitude of variables that can affect the drilling performance, only some of which are controllable and/or measurable. Additionally or alternatively, improved systems and methods may be adaptive to react to changes in drilling conditions in real time, such as responding to lithology changes or other uncontrollable changes in drilling conditions. When an abnormal drilling event happens, improved systems and methods may be able to detect it at its emergence and generate recommendations to mitigate the problem. Accordingly, the need exists for systems or methods to improve drilling performance measured by factors more robust and indicative than just the rate of penetration. Additionally or alternatively, the need exists for systems or methods for improving drilling performance by controlling at least two controllable drilling variables. In some implementations, recommendations for the control of such controllable drilling variables may be generated and/or implemented in at least substantially real-time during ongoing drilling operations. The present invention provides systems and methods to provide one or more of these improvements and/or to satisfy one or more of these needs.